I. Field of the Invention
The present invention relates generally to soil enhancing compounds, and more particularly to those soil enhancing compounds which employ phosphogypsum and similar industrial by-products as a source of phosphorous, as well as the method for producing such compounds.
II. Description of the Prior Art
The disposal of waste products in general is an ever-increasing worldwide concern. Public demand and government regulations have called for safer and more effective storage and disposal of these wastes. Nearly all production processes, including agricultural and industrial processes, and municipal water treatment, produce waste by-products.
The production of chemicals is a long practiced and still growing industry in Louisiana. As with almost every industrial process, both acidic and alkaline by-products are generated. In the industrial corridor on the Mississippi River between Baton Rouge and New Orleans, there exist numerous chemical plants and stock piles of waste products. One specific and seriously polluting type of waste is a by-product created in the production of phosphate fertilizers and phosphoric acid. The common process for extracting phosphate is known as the "wet acid process". Phosphate-containing rocks, composed mostly of calcium phosphate, are exposed to water and sulfuric acid yielding phosphoric acid and phosphogypsum. For each ton of phosphoric acid produced by the wet acid process, there are approximately five (5) tons of phosphogypsum produced. This acidic waste, referred to as phosphogypsum slurry, with a typical pH of 2 to 3, is pumped into large piles. The storage of this phosphogypsum causes many environmental problems, and the present method of storing has several disadvantages. First, the natural flow of rain water through the material may create acid runoff and accidental contamination of ground water. Second, phosphogypsum is inherently radioactive, depending upon the type of rock used and the location from which the rock was mined. As a result, phosphogypsum typically contains approximately 25 picocuries of radium-226 per gram (pCi/gram) or higher. Moreover, radon gas, released as part of the normal radium decay process, has become the major radionuclide cause for concern. EPA regulations currently state that for handling phosphogypsum, the average concentration of radium-226 shall not exceed 10 pCi/gram of substance handled.
The industrial response to these ever-growing stockpiles of phosphogypsum has been to devote increasing funds toward research in storage of the materials. If it is stored for long enough periods of time, e.g. about 400 years, the radioactive material will simply decay to a point when it is no longer dangerous to handle. However, such continued use of these methods prevents the industries from realizing the potential uses and benefits of phosphogypsum, as well as similar wastes which contain calcium sulfate and phosphorous, in other applications. New methods and products are needed which capitalize on the recoverable elements within these industrial by-products in a way that minimizes most of the concerns surrounding the radioactivity of the waste.
Southern Louisiana is also a leader in the production of sugar cane, rice and other crops, thus creating considerable quantities of agricultural by-products. Examples of such by-products are bagasse, rice hulls, corn husks, and cotton gin waste. As is the case of the industrial waste just described, the prevailing method of disposal is stockpiling. Many of these stockpiles are unmanaged and also represent a source of surface water pollution. When appreciable quantities of runoff from these agricultural by-products are left to enter lakes, streams, and other bodies of water, the biochemical oxygen demand (BOD) on the aquaculture can result in the loss of valuable plant and animal resources. Despite these hazards, such materials, when processed properly, can greatly benefit the environment when used in combination with other chemicals.
A third by-product produced in large quantities, in nearly all communities, is municipal waste water treatment residue. During the process of water and waste water treatment, there is usually an alkaline residue created as a result of the filtration process. This is referred to in the industry as waste sludge or "bio-solids" and often comprises the used filter cakes formed on the treatment filters during filtration. In many cases, these bio-solids require costly methods of disposal, such as through landfills and incineration. What is needed is a way of combining all of the above-described waste materials into a safe and usable product that can actually enhance the environment, rather than damage it through inadequate methods of disposal.